Aristotle, Galileo and Newton and Newton’s Laws of Motion

1. Aristotle, Galileo and Newton and Newton’s Laws of Motion Chapter 3.1-3.6 Chapter 6.1-6.3 Chapter 7.1-7.4

2. ARISTOTLE 384 BC – 322 BC Ancient Greece One of the first to try to explain the natural world Geocentric view of the universe Ideas based on observations that seemed to be true

3. GALILEO 1564 – 1642 Italy Perhaps the first true scientist. Rolled and dropped objects to discover the true aspects of motion

4. NEWTON 1642-1727 England Developed laws for motion and gravity that explain why objects move, and worked with optics

5. 3.1Aristotle on Motion • Objects do not move without a force. • Objects in motion always require a force to keep them moving. • Objects seek their natural state, which is at rest. • Mechanical equilibrium can only be static.

6. 3.1 Galileo and Newton on Motion • Objects do not change motion without unbalanced force. • Objects in motion do not always require a force to keep them moving. • Objects have two “natural” states of motion, at rest (static equilibrium) and moving at a constant speed and direction (dynamic equilibrium). Simply put, things tend to keep on doing what they’re already doing.

7. 3.4Newton’s Law of Inertia Is a force required to keep an object moving? Newton’s first law, usually called the law of inertia, is a restatement of Galileo’s idea that a force is not needed to keep an object moving. • Galileo argued that only when friction is present is a force needed to keep an object moving. • Galileo stated that if friction were entirely absent, a ball moving horizontally would move forever at the same speed and in the same direction (at a constant velocity).

8. 3.4Newton’s Law of Inertia The law of inertia provides a completely different way of viewing motion from the ancients. • Objects continue to move by themselves. • Forces are needed to overcome any friction that may be present and to set objects in motion initially. • Once the object is moving in a force-free environment, it will move in a straight line indefinitely.

9. The First Law of Motion • Objects at rest stay at rest and objects in motion stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. (also called the law of inertia). • Inertia: the tendency of an object to resist acceleration • Inertia is not a force, it’s a property of matter. • More mass, more inertia

10. The Second Law of Motion The net force equals mass times acceleration. Fnet = ma or a = Fnet/m Explains the relationship between Net force, mass and acceleration (direct vs. inverse relationships) In the presence of a net force (greater than zero) an object will experience acceleration

11. The Third Law of Motion For every action force, there is an equal and opposite reaction force. Forces act in pairs!

12. 6.1Force Causes Acceleration What causes an object to accelerate? Unbalanced forces acting on an object cause the object to accelerate. Net Force > 0

13. 3.3Galileo on Motion think! A ball is rolled across a counter top and rolls slowly to a stop. How would Aristotle interpret this behavior? How would Galileo interpret it?

14. 3.3Galileo on Motion think! A ball is rolled across a counter top and rolls slowly to a stop. How would Aristotle interpret this behavior? How would Galileo and Newton interpret it? Answer: Aristotle would say that the ball stops because it seeks its natural state of rest. Galileo and Newton would say that the friction between the ball and the table overcomes the ball’s natural tendency to continue rolling—overcomes the ball’s inertia—and brings it to a stop.

15. 3.3Galileo on Motion According to Galileo and Newton, when is a force needed to keep an object moving? Only when friction (or some other oppositional force) is present is a force needed to keep an object moving.

16. 3.4Newton’s Law of Inertia Objects at Rest • Objects in a state of rest tend to remain at rest. • Only a force will change that state.

17. 3.4Newton’s Law of Inertia Objects in Motion • In the absence of forces, a moving object tends to move in a straight line indefinitely. • Toss an object from a space station located in the vacuum of outer space, and the object will move forever due to inertia.

18. 3.4Newton’s Law of Inertia Objects at rest tend to remain at rest.

19. 3.4Newton’s Law of Inertia

20. 3.4Newton’s Law of Inertia

21. 3.4Newton’s Law of Inertia think! A force of gravity between the sun and its planets holds the planets in orbit around the sun. If that force of gravity suddenly disappeared, in what kind of path would the planets move?

22. 3.4Newton’s Law of Inertia think! A force of gravity between the sun and its planets holds the planets in orbit around the sun. If that force of gravity suddenly disappeared, in what kind of path would the planets move? Answer:Each planet would move in a straight line at constant speed.

23. Does this statement make sense? • The weight of a 200 g mass is 1.96 N.

24. Friction Lab • Due at end of period: • Data Table • Save two graphs onto desktop • staticFrictP1last name • Kinetic Frict p1 last name • Use logger pro on laptop to create two separate graphs and find slope using analyze/linear fit • normal force vs. static max friction • Normal force vs. kinetic friction